This invention relates to a pressure cylinder such as a master cylinder, primarily for use in a vehicle brake or clutch hydraulic system, and particularly to such a cylinder molded from plastics material and having a surrounding body, such as a mounting flange, serving for the attachment of the assembly to a support.
Proposals have already been made for the production, by molding from plastics material, of a pressure cylinder having an integral surrounding body in the form of a mounting flange. However, because the mounting flange of such a cylinder is usually of significantly greater thickness than the cylinder wall, differential contractions occur upon cooling after molding, which can result in cylinder bore distortion in the region of the flange. Such distortion can create problems in maintaining an adequate seal between the cylinder internal wall and an internal co-operating piston assembly and can also result in the snagging of the piston and/or its associated seals and possible consequent jamming of the piston assembly within the cylinder.
One attempt to solve this problem consists in mounting the flange by way of an outer cylindrical formation generally co-axial with and surrounding the cylinder proper, said formation being connected to the cylinder at a position beyond the inward limit of piston travel. This arrangement removes any bore distortion resulting from the flange molding to a location at which it does not significantly adversely effect the travel or sealing of the piston assembly. However, unless the cylindrical formation carrying the flange is made relatively short, there is a risk of untoward flexing of the formation and consequent movement of the cylinder taking place during operation of the master cylinder, in use. Alternatively, by making the formation as short as possible, an undesirably long portion of the cylinder extends rearwardly of the flange and can be difficult to accommodate. Thus, although this approach can produce a satisfactory practical cylinder, it introduces restrictions upon the cylinder design and associated molding process, as well as requiring extra material, all of which leads to additional manufacturing cost.